Migration from the old version of Google Analytics, "Universal Analytics (UA)," to the new version "GA4" has already been completed on many sites. On the other hand, there are also cases of "not yet migrated to GA4" on sites that have not been updated for a long time or on newly handed-over projects. This article organizes the current situation that forms the premise of UA-to-GA4 migration, then explains the migration (GA4 setup) procedure and the points to note during migration.
Premise: UA Has Already Ended
The first thing to understand is that UA has already ended its service. Free UA stopped processing new data on July 1, 2023, and after the subsequent transition period, access to the UA admin screen and data also ended (the paid version, Google Analytics 360, also ended measurement in October 2023).
Therefore, at present, the task of "migrating from UA to GA4" does not strictly mean carrying over UA's data, but refers to newly creating a GA4 property and starting measurement. UA and GA4 have fundamentally different data models, and automatic migration of past data was not possible to begin with. For sites where GA4 measurement has not yet started, it is important to set up GA4 as soon as possible so as not to widen the data gap any further.
The Main Differences Between UA and GA4
Understanding the difference in thinking between UA and GA4 before proceeding with migration makes it less confusing to read the data after setup.
Measurement centers on "events": UA measured around page views and sessions, but GA4 captures all user actions as "events."
Measures across web and app: GA4 integrates website and app data and can analyze on a per-user basis.
Metric definitions have changed: The way sessions and users are counted has changed, so even metrics with the same name differ in value from UA.
Data retention period has shortened: UA was up to 50 months, but GA4 is up to 14 months (the default is 2 months).
UA-to-GA4 Migration (GA4 Setup) Procedure
Here we introduce the basic flow from creating a GA4 property in the Google Analytics admin screen to starting measurement. Screen names may change with updates on Google's side, so proceed by reading them as the latest display.
Create a GA4 property: Log in to Google Analytics and, from "Admin," use the "GA4 Setup Assistant" to create a GA4 property. Set the property name, time zone (Japan), currency (Japanese yen), and so on.
Set up a data stream: Choose the platform to measure (web), enter the site URL and stream name, and create a data stream. A "Measurement ID" is issued here.
Install the Google tag (measurement tag): Based on the issued Measurement ID, install the measurement tag on the site. There is a method of adding a GA4 configuration tag in Google Tag Manager (GTM) and a method of installing gtag.js directly. With a CMS such as WordPress, it may be enough to just enter the Measurement ID from a plugin or settings screen.
Check that measurement is working: In GA4's "Realtime" report, check whether your own access is counted. If data appears, measurement has started.
Change the data retention period: From "Admin" → "Data Settings" → "Data Retention," change the event data retention period from the default 2 months to 14 months.
Points to Note During UA-to-GA4 Migration
Past Data Cannot Be Carried Over
UA data cannot be carried over to GA4. If you want to do comparative analysis such as year-over-year comparisons, you need to wait until enough data has accumulated in GA4. The sooner you start measuring on a site you are setting up from now on, the more it leads to future analysis.
Don't Compare Numbers as if They Were UA
Because UA and GA4 differ in their measurement thinking, numbers such as session count and conversion count do not match even with the same name. Comparing directly with UA-era reports leads to mistaken judgments, so it is important to re-grasp GA4 on its own terms.
Watch for Tag Duplication or Misplacement
When installing tags directly with gtag.js or using a CMS plugin, be careful not to mistake the tag placement. Accidentally overwriting an existing tag or installing a measurement tag twice can prevent data from being collected correctly. After installation, always check the measurement status with the realtime report or similar.
Don't Stop at Initial Setup
Simply creating a GA4 property does not guarantee that you can do the analysis your business truly needs. It becomes a practical analysis foundation only when you arrange initial settings such as configuring important actions (inquiries, purchases, etc.) as conversions (key events) and linking with Google Tag Manager and advertising services.
Summary
UA-to-GA4 migration, now that UA has already ended, means "the task of newly creating a GA4 property and starting measurement." Because UA's past data cannot be carried over, it is important for sites that are not yet measuring to set up GA4 even a day sooner and begin accumulating data.
As for the procedure, the basic flow is creating a GA4 property, setting up a data stream, installing the measurement tag, checking measurement, and changing the data retention period. While being careful about the differing premises of the numbers from UA and about tag installation mistakes, doing the initial adjustments such as conversion settings lets you make use of GA4 as a practical analysis foundation. Start by checking whether GA4 is measuring correctly on your own site.
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